Fencing systems that use a virtual barrier, rather than a physical barrier, to restrict the location and movement of animals are known in the art. There are two basic types of “virtual” fencing systems.
One type of virtual fencing system employs a buried wire that defines a containment perimeter. The wire radiates a signal that is sensed by a device worn by a monitored animal. As the monitored animal approaches the perimeter, the signal is sensed and the device delivers a correction (e.g., typically sound or an electric shock) to the animal to dissuade it from breaching the perimeter.
The other type of virtual fencing system uses a wireless positioning system, such as GPS, to establish a perimeter and determine an animal's location. An example of such a “wireless” fencing system is disclosed in U.S. Pat. No. 6,581,546 (“the '546 patent”).
According to the '546 patent, a control unit that includes a GPS positioning receiver, a means for applying a correction, and suitable control and logic circuitry/software is attached to an animal's collar. In conjunction with the control unit, a user establishes a containment perimeter. The perimeter is defined by positional coordinates, which are obtained from the GPS positioning receiver. In use (after the perimeter is defined), the control unit compares the position of the receiver (i.e., the position of a monitored animal) with the containment perimeter. As the animal approaches the perimeter, as determined by the comparison, a correction is applied. If the animal breaches the perimeter, the control unit expands the perimeter in a further attempt at containment. The system attempts to redirect the movement of the animal toward the original containment zone using additional corrections as necessary. Further perimeter breaches are addressed by continued perimeter expansion. If the animal changes direction toward the original containment zone, the expanded perimeter is then contracted behind the animal.
One benefit of a wireless fencing system, relative to buried-wire systems, is that the wireless fencing system has the ability to dynamically change the perimeter in order to regain control of an animal after a breach. Once breach occurs in a buried-wire system, the ability to control the animal is lost. A second benefit of a wireless fencing system over a buried-wire system is that there is no disincentive in a wireless fencing system to re-cross a breached perimeter. In particular, if an animal attempts to return to the original containment zone in a buried-wire system, it will be corrected as it nears the wire. This provides a disincentive to return to the containment zone. In contrast, in a wireless system, the perimeter can be reestablished behind a returning animal so that he will not be corrected or otherwise dissuaded from returning to the original confinement zone.
There are, however, some drawbacks to wireless fencing systems, such as the one described in the '546 patent. One drawback is that when an original perimeter is expanded in response to a breach, a “free” zone in which the animal is permitted to roam is established between the original perimeter and the expanded one. This might place an animal in jeopardy by allowing it to reach dangerous areas that it could not otherwise access from the original confinement zone.
A second drawback of some wireless fencing systems is that they implicitly rely on untested assumptions about the animal's return path. In particular, some wireless fencing system create a sequence of small confinement zones (rather than a simple expanded perimeter) to herd to the original confinement zone. This sequence of small zones is assumed to provide a safe return path based solely on the fact that the animal traversed that route on its outbound journey. But that path might not be safe and it might not be the shortest route back to the original containment zone.
A third drawback of some wireless fencing systems is that the programming interface (e.g., a button, etc.) is located on the control unit that is attached to the animal's collar. To the extent that an animal that is wearing a control unit is exposed to rain, mud or free-standing water, as might occur when the animal is outside in inclement weather, the internals of the control unit can malfunction, thereby shortening the life of the control unit.
A need exists, therefore, for a wireless fencing system that avoids one or more of the disadvantages of the prior art.